1. Field of the Invention
The present invention relates to a guidance system for a self-advancing vehicle such as a floor washing machine, which is arranged to control the traveling direction of the self-advancing vehicle along a guidance line drawn along a predetermined traveling path on a floor surface.
2. Related Background Art
Self-advancing vehicles that perform various operations without an operator while automatically traveling on a floor surface, for example such as automatic floor washers, vacuum cleaners, or carrying vehicles, are known. One such conventional guidance system for automatically controlling the traveling direction is described in Japanese Published Patent Application No. 57-128119 to Isamu. It teaches a system for guiding the self-advancing vehicle used a photosensor attached to the self-advancing vehicle that detected reflected light from a reflective tape which was previously adhered onto the floor surface along an intended traveling path.
The above guidance system with reflective tape, however, had such problems that the reflective tape was conspicuous and spoiled the beauty. Particularly in the case of floor washers, a rotary brush could abrade or peel off the reflective tape. That required frequent tape exchange, and thus created problems for wide areas.
There was another conventional system described in Japanese Published Patent Application No. 3-237958 to Hidetaka et. al. in which a laser source was set on the ceiling to emit a laser beam toward the floor surface. The traveling direction was controlled by detecting the laser beam using a photosensor mounted on the self-advancing vehicle.
This laser beam guidance system, however, had problems in that costs for apparatus and installation were high and that it could become disabled when the laser beam was interrupted by an obstacle or the like.
Japanese Published Patent Application No. Hei 2[1990]-56610 to Toshihiro et al. teaches an optical guidance system for moving vehicles. A guide path is coated with a strip of transparent paint that selectively absorbs or reflects light outside of the visible range. A series of three sensors detects light absorbed or reflected from the paint to keep the moving vehicle following the paint line. The center sensor detects the paint strip. The other two sensors monitor the unpainted floor and detect when the vehicle is moving off the paint strip. They steer the vehicle back to following the paint strip. One problem with this system is that dirt on the floor makes it harder for the sensors to keep the vehicle following the paint strip because the dirt makes the paint strip harder to distinguish from the floor next to the strip.